All fiber optic current sensor based on phase-shift fiber loop ringdown structure.

An all fiber optic current sensor (AFOCS) utilizing ordinary optical fiber is proposed and demonstrated, which is implemented with a phase-shift fiber loop ringdown (PS-FLRD) structure. The current-induced rotation angle is converted into a minute change in transmittance of the fiber loop, which can be obtained by measuring the phase shift. The current sensitivity is improved by allowing optical signals to traverse the sensing fiber repeatedly. The relationship between the current sensitivity, intrinsic phase shift, and initial transmittance of the fiber loop is numerically analyzed, and the tunable sensitivity is experimentally verified by adjusting the modulation frequency. An optimal current sensitivity of 0.8158°/A is experimentally obtained for the proposed sensor, and the minimum detectable current is at least 100 mA. The proposed sensor requires fewer polarization elements compared with the common type of fiber optic current sensor (FOCS) and has the characteristics of simple structure, high sensitivity, and ease of operation; it will be a promising approach in practical applications.

Design of multifunctional all-optical logic gates based on photonic crystal waveguides.

The explosive development of the big data era has driven the rapid growth of silicon photonics, and logic operators based on photonic circuits have also been intensively investigated. Photonic integrated logic operators possess a high degree of design freedom and novel prospects, and they are regarded as promising platforms for future signaling and data processing. In this work, considering all-optical logic operation with lower power consumption and a smaller device footprint, multifunctional all-optical logic gates based on silicon photonic crystal (PhC) waveguides and phase-encoded light beams are proposed and applied to realize several logic operators, including XNOR, XOR, NOR, AND gates as well as a half adder and half subtractor. The initial phases (π and 0) of incident light represent the input digital states (1 and 0), and the logic operation results are determined by the output light intensity. Also, simulations are carried out to verify the proposed concept and to investigate the rise time, fall time, and cross talk of the devices. Theoretically, the bit rate for the proposed device can reach 1.25 Tb/s, and the proposed structures have the potential to be extremely compact due to PhC waveguides.